The present invention relates to wireless communication systems that utilize Orthogonal Frequency Division Multiplexing (OFDM), and more particularly to methods and apparatuses for processing sub-carriers in a receiver in an OFDM communication system.
Examples of systems utilizing OFDM are those configured in accordance with wireless local area network (WLAN) standards IEEE 802.11a or 802.11g as well as those configured in accordance with any of a number of standards for broadcasting information, such as those for Digital Video Broadcasting (e.g., DVB-T, DVB-H, T-DMB), and for Digital Audio Broadcasting (DAB). OFDM is also the chosen access technique for the long term evolution in the Third Generation Partnership Project (3GPP) (3GPP-LTE).
In an OFDM system, data is transmitted in parallel on a large number of orthogonal sub-carriers. Efficient implementations of OFDM transmitters employ an inverse fast Fourier transform (IFFT) to generate the signal to be transmitted from parallel data streams. The parallel data streams are supplied as inputs to the IFFT, and the signal to be transmitted is supplied at the output.
OFDM technology is efficiently implemented in the receiver by employing a fast Fourier transform (FFT) to process the parallel data streams (one data stream per sub-carrier) from the received signal. Typical sizes of the FFT range from 64 (for instance for WLAN) to 8192 (for instance for DVB-T). If the size of the FFT is N, then the N samples at the output of the FFT are collectively referred to as an OFDM symbol. The number of sub-carriers used for data transmission is typically between 0.5N and N, where N is the FFT size.
One of the major reasons for using OFDM is that the channel estimation and equalization in the receiver can be performed by algorithms/circuitry whose level of complexity is much lower than that which would be required if a single carrier transmission were to be employed. Notwithstanding this generally lower level of complexity, the channel estimation and equalization are among some of the most computationally intensive blocks in an OFDM receiver. This is because the channel is essentially estimated for each one of the sub-carriers and its effect equalized on a sub-carrier by sub-carrier basis.
It is therefore desirable to provide methods and apparatuses for more efficient OFDM signal reception.